Ayaka Shiomura, a member of the Tokyo assembly, was told to get married while she tried to debate support for childrearing. Photograph: Jiji Press/AFP/Getty Images

Senior Japanese politicians have urged the Tokyo city government to "clean up its act" after an assemblywoman was subjected to sexist abuse during a debate on support for childrearing.

The incident drew criticism from across the political spectrum after unidentified male assembly members, all thought to belong to the conservative Liberal Democratic party (LDP), shouted abuse at Ayaka Shiomura as she questioned the city administration's commitment to helping pregnant women and young mothers, as Japan attempts to tackle its low birthrate.

One shouted: "You're the one who should get married as soon as possible." Another asked if she was able to have children, prompting laughter among other male councillors.

Colleagues of Shiomura, a 35-year-old member of the centre-right Your party, demanded that the hecklers be identified and punished. The LDP's Tokyo chapter did not deny the remarks were made but said there was insufficient evidence to punish individual councillors.

The outbursts are an embarrassment to the prime minister and leader of the LDP, Shinzo Abe, who is pushing to increase the number of women in senior positions in business and improve Japan's poor standing in global gender equality rankings.

The chief cabinet secretary, Yoshihide Suga, said the behaviour of LDP representatives in the Tokyo assembly was not a reflection of the party's national policies. He added: "If there were comments of a sexist nature, I would like the assembly to clean up its act."

The health minister, Norihisa Tamura, whose portfolio includes promoting women in the workplace, said the abuse was "deeply disrespectful to women". Masako Mori, the minister responsible for tackling the low birthrate, described the comments as "totally unacceptable".

Shiomura and her party colleagues were unable to identify the hecklers, but said the comments had originated in a section of the assembly chamber occupied by members of the LDP.

Eyewitnesses said Shiomura had been reduced to tears by the intervention, but continued with her remarks.

"The male members' offensive remarks indicate they think women who aren't married, or can't bear a child, aren't worth listening to," Shiomura told the Wall Street Journal. "For such male members, understanding and making policies for women who want to but can't marry or have children would be difficult."

The incident unleashed an outpouring of indignation on social media and a flurry of angry phone calls to the Tokyo metropolitan government. As of noon on Friday, 35,000 people had signed an online petition calling on the LDP's Tokyo chapter to name the culprits and administer a "severe punishment".

Shiomura's post describing her ordeal had been retweeted more than 20,000 times by Thursday evening. One woman urged her to establish the identity of the hecklers "so I can make sure I never vote for them again".

The composition of the Tokyo assembly reflects the under-representation of women in positions of influence in Japan. Just 27 of the chamber's 127 representatives are female. All but 78 of the 772 seats in the upper and lower houses of parliament are occupied by men.